From Wikipedia:
The adult male has a cinnamon-red head and body with a brown back, a red eye and a dark bill. The adult female has a mottled brown body, a pale brown head, brown eyes and a grey bill and is very similar in appearance to a female blue-winged teal; however its overall color is richer, the lore spot, eye line, and eye ring are less distinct. Its bill is longer and more spatulate. Male juvenile resembles a female cinnamon or blue-winged teal but their eyes are red.